Field of the Invention
The presently disclosed subject matter relates to facilitating the flow of streams within vessels utilized in the process industry.
Description of Related Art
The number of bed vessels installed and operating in industry totals in the tens of thousands worldwide. Bed vessels are usually large with diameters ranging from 4 to 18 feet and heights from 10 to over 100 feet. The volume of such bed vessels is substantially filled with bed vessel internals. Each year, the number of bed vessels that are shutdown or are constructed and commissioned totals in the hundreds. The designed lifetime of these bed vessels is typically measured in decades. Bed vessels used in industry contain appropriate internals which can include one or more beds of solid processing material elements which facilitate intended processing operations. Such solid processing material elements can include, for example, reaction-promoting catalysts and mass transfer-promoting agents including sieves and sorbents. Bed vessels and their contents represent a very sizable investment by the bed vessel owner.
The normal length of a typical bed vessel “on oil” operating cycle (from vessel startup to vessel shutdown) is measured in months or years. Normal operations are usually halted when bed vessel internals reach performance limits or when bed vessel operating conditions, such as temperature or pressure, exceed operating limits. Such shutdowns are typically followed by rejuvenation of, repair to and/or replacement of bed vessel internals followed by restart of operations.
It is known in the art to utilize suitable materials to promote flow distribution for streams entering bed vessels. The purpose of such distribution is to subdivide the streams into rivulets which improve stream contact with bed vessel processing materials. Three dimensional reticulates are known to promote flow distribution. For example, U.S. Pat. Nos. 6,258,900, 6,291,603 and 7,265,189 each describe such reticulated materials.
Many bed vessels face challenges associated with sustaining effective and efficient utilization of bed vessel internals including effective and efficient stream flow distribution across and throughout the beds of solid processing material elements installed in the bed vessels. Inadequate stream flow distribution leads to coalescence of small stream rivulets into larger streams resulting in stream flow channeling which can result in bypassing portions of the bed vessel processing internals.
Stream flow channeling within a bed vessel can occur and change over time due to shifts in operating conditions (e.g., changing compositions of feed streams), operations upsets (e.g., power surges/cuts, pump failures, etc.), natural or accelerated aging of bed vessel internals and the like. Channeling can occur when coalescence is facilitated by smaller fluid streams contacting each other or by contact with other bed vessel internals or with the bed vessel itself. Channeling is undesirable because it results in areas of underexposed and underutilized bed vessel internal materials and areas of overexposed materials. The former can result in significant loss of bed vessel productivity and profitability. The latter can result in so-called “hot spots” where sharp temperature gradients cause damage to the vessel and its internals.
One approach to coping with these situations has been to tolerate moderate bed vessel underperformance and operate the vessel until performance has degraded to an unacceptable level. At such a time, the bed vessel is shutdown so that bed vessel internals can be adjusted, rejuvenated or replaced. This mode of operation results in reduced “on-oil” operating time with accompanying loss of bed vessel productivity and profitability.
Another approach has been to install one or more conventional structured engineering devices at appropriate locations within the bed vessel to facilitate flow redistribution within and across the cross section of bed vessels and, in doing so, increase stream flow contact with bed vessel internals (including beds of solid processing materials) and reduce the negative consequences of stream flow channeling. Such conventional devices include engineered equipment structures that are typically form-fitted to the inside of the bed vessel and which can occupy up to ten feet of depth within the bed vessel. Such devices are costly to design, fabricate, install, operate and maintain and requires specially-trained personnel to do so. These conventional devices also require complex monitoring and containment systems to ensure segregation from other bed vessel internals. In the example of catalytic reactors, this applies to segregating conventional redistribution devices from catalyst via “catalyst containment” equipment and measures. Any loss of catalyst containment can result in process and safety risks. Considerable measures are taken and bed vessel space dedicated to ensuring that catalyst containment is ensured. The very presence of such conventional redistribution and containment equipment and the difficulty of sustaining their stable and controlled operation can lead to problems up to and including development of bed vessel shell hot spots leading potentially to rupture of the bed vessel itself.
The very presence of such conventional structured engineered devices consumes space that could otherwise be consumed by more productive and more profitable bed vessel internals, such as catalyst. An example of such a structured engineered apparatus and its use as a flow distributor is shown in U.S. Pat. No. 7,314,551 granted Jan. 1, 2008 to UOP, LLC of Des Plaines, Ill.
Improvements in this field of technology are desired.